The present apparatus and method relate generally to the fabrication of a transition duct from a grooved sheet of fibrous board and more particularly to apparatus and method for making transition cuts in a grooved sheet of fibrous board.
The use of densified glass fiberboards for air conditioning and other duct work is well-known. Such boards usually are continuously manufactured by apparatus which progressively densifies and heat cures a blanket or mat of binder impregnated glass fibers. Such boards may be as much as two inches thick after densification and may be as wide as eight feet or more. An outer cover for the duct to be formed from the board is adhered to the bottom surface of the board. This cover or skin often comprises a layer of Kraft paper adjacent the glass fibers, a second outer layer of a scrim-like fabric and an outermost layer of an air impervious material, such as aluminum foil, vinyl film, or the like. An example of such a board is that product sold and marketed by Johns-Manville Corporation as MICRO-AIRE Duct Board.
After the fireboard has been provided with its outer skin, it is conventional to cut, by an installer or by machinery, a set of laterally spaced apart, longitudinal grooves in the fireboard. Typical is the shiplap groove shown in FIG. 6 of the instant specification, which groove has been cut so as to remove most of the glass fiberboard leaving a thin layer adjacent its skin so that the board can be folded along the grooves upon itself to form a hollow rectangular configuration.
It is also known in the duct construction field that a transition piece, that is, a duct which has sidewalls which taper such that one duct end has a smaller transverse cross-section than the other end, may be fabricated from the precursor grooved board by cutting from the board at locations adjoining the grooves appropriately sized wedge-shaped pieces of the fiberboard. For example in a typical "one-way" transition i.e., one involving either a change in duct depth or width, entails removal of a wedge of material from each of two of the four rectangular panels that comprise each grooved sheet.
Heretofore in the preparation of transitions, a grooved sheet of fiberboard is placed upon a flat work surface, most commonly with the female edge of the sheet towards the fabricator, whose basic tools include a marking pencil, an incrementally marked straightedge, and a cutting knife which has a sharp edge, a blunt edge and a flattened portion. In preparing a common "one-way" transition, for example, cutting marks are made upon the appropriate first panel and upon the opposite edge side of the equivalent panel e.g. the top and bottom panel of the duct. Using the straightedge as a measuring device, a mark reflecting the axial extent of the tapering portion of the duct is made at a point on a side edge of a first panel, and a second mark, corresponding to the desired change of duct depth or width is made at an appropriate point at the leading, or female edge of this first panel. The straightedge is aligned with the two marked points and held in place, and the cutting knife is drawn along the straightedge, cutting all the way through the glass fiber as well as the cover material. Using the blunt and slightly rounded edge of the knife, a second cut which scores the glass in the bottom of the deep part of the groove but not the underlying cover material, is made along the groove from the point of intersection with the first cut, to the leading edge of the sheet. Using the flat surface of the knife the resulting wedge-shaped piece of glass fiber is separated from the underlying flap of covered material and the glass material is removed. For a one-way transition the opposite side of the panel equivalent to the first panel is correspondingly marked and cut. A drawback in using the above-described tools and method for making transition cuts is in the time consumption involved, which problem is aggravated when one is presented with the more numerous measuring operations that are necessary for fabrication of the more complex transitions such as the "focal" transition in which two transition cuts must be made in each of the four panels comprising the sheet of fiberboard. It has also been found that the fair amount of hand and visual judgments involved in marking distances and aligning the straightedge between markings limit the accuracy and quality of the transition.
It is therefore the principal object of the instant invention to provide a method and apparatus for the quick and simple making of the necessary measurements for transition cuts in grooved sheets of fiberboard and the aligning of a cutting edge of guiding a cutting tool in making the cuts.
It is another object of the invention to provide an apparatus and method for controlling the accuracy and quality of transition cuts.